Page:Popular Science Monthly Volume 1.djvu/559

 Rh more delicate means of dealing with the matter. The rainbow-tinted streak forming a star's spectrum is crossed by known dark lines; and these serve as veritable mile-marks for the spectroscopist. If one of these lines in the spectrum of any star is seen to be shifted toward the red end, the observer knows that the star is receding, and that swiftly; if the shift is toward the violet end, he knows that the star is swiftly approaching

Now, Dr. Huggins had been able nearly four years ago to apply this method to the case of the bright star Sirius, though his instrumental means were not then sufficient to render him quite certain as to the result. Still he was able to announce with some degree of confidence that Sirius is receding at a rate exceeding 20 miles per second. In order that he might extend the method to other stars, the Royal Society placed at his disposal a fine telescope, 15 inches in aperture, and specially adapted to gather as much light as possible with that aperture. Suitable spectroscopic appliances were also provided for the delicate work Dr. Huggins was to undertake. It was but last winter that the instrument was ready for work; but already Dr. Huggins has obtained the most wonderful news from the stars with its aid. He finds that many of the stars are travelling far more swiftly than had been supposed. Arcturus, for example, is travelling toward us at the rate of some 50 miles per second, and, as his thwart-motion is fully as great (for this star's distance has been estimated), the actual velocity with which he is speeding through space cannot be less than 70 miles per second. Other stars are moving with corresponding velocities.

But, amid the motions thus detected, Dr. Huggins has traced the signs of law. First he can trace a tendency among the stars in one part of the heavens to approach the earth, while the stars in the opposite part of the heavens are receding from us; and the stars which are approaching lie on that side of the heavens toward which Herschel long since taught us that the sun is travelling. But there are stars not obeying this simple law; and among these Dr. Huggins recognizes instances of that community of motion to which a modern student of the stars has given the name of star-drift. It happens, indeed, that one of the most remarkable of these instances relates to five well-known stars, which had been particularly pointed to as forming a drifting set. It had been asserted more than two years ago that certain five stars of the Plough or Charles's Wain—the stars known to astronomers as Beta, Gamma, Delta, Epsilon, and Zeta, of the Great Bear—are drifting bodily through space. The announcement seemed to many very daring, yet its author (trusting in the mathematical analysis of the evidence) expressed unquestioning confidence; he asserted, moreover, that whenever Dr. Huggins applied the new method of research, he would find that those five stars are either all approaching or all receding, and at the same rate, from the earth. The result has justified his confidence as well in his theory as in Dr. Huggins's mastery of the new method. Those